Use of unripe grapes harvested during cluster thinning as a method for reducing alcohol content and pH of wine

Abstract

Background and Aims: Deep red full-bodied wines can only be obtained from grapes with complete phenolic maturity, which frequently produce wines with high pH and alcohol content. The present study focuses on a new procedure for simultaneously reducing pH and ethanol content. Methods and Results: Grapes from cluster thinning were used to produce a very acidic low-alcohol wine. The wine was treated with high doses of charcoal and bentonite. This odourless and colourless wine was used to reduce pH and ethanol content of wine produced from grapes, which had reached complete phenolic maturity. The anthocyanin and proanthocyanidin concentrations, the mean degree of polymerisation and the monomeric composition of proanthocyanidin of reduced-alcohol wines were similar to those of their corresponding controls. Since the pH was lower, the colour of the reduced-alcohol wines was more intense. No significant differences were found between reduced-alcohol wines and their controls by triangle sensory tests using dark glasses for two of the three studied cultivars. Conclusion: The procedure described allowed production of wines with reduced alcohol content and pH, while retaining similar phenolic content and sensory properties. Significance of the Study: The proposed procedure is easy to apply, does not require specific equipment and offers a means of addressing the problem of wines developing high ethanol and low pH as a result of over-ripening of grapes. © 2011 Australian Society of Viticulture and Oenology Inc.